Extra-High Temperature High Density Cement Slurry for Cementing Liners through Salt Formation in Well Qieshen-1

The well Qieshen-1 is an exploration well deployed by Sinopec in block Tazhong in Tarim Basin. The well was drilled to a depth of 8,745.00 m in four intervals, with static bottom hole temperature being 196 ℃. Technical difficulties such as high temperature, high pressure, salt formation, narrow clearance between the wall of the hole and the casing string as well as difficulties in displacing the whole-oil based drilling fluid were encountered in cementing the casing string in the fourth interval. To deal with these difficulties, studies were conducted on the strength decay of the set cement and the settling stability, rheology and thickening time of the cement slurry. A saltwater resistant high density (Max. density 2.3 g/cm³) cement slurry that is stable at 230 ℃ was developed as a result of the study. Using aluminum-rich materials in the cement slurry, the decay of the strength of the set cement is inhibited. The settling stability of the cement slurry is improved by selecting weighting materials of different particle sizes, and silica fume. Other additives, such as high temperature filter loss reducers, compounded retarders and polyether-carboxylic acid dispersants were used to adjust the properties of the cement slurry to the required levels. Laboratory experiments show that the API filtration rate of the cement slurry is 44 mL, the flow index n is greater than 0.7, the thickening time is linearly adjustable, the high temperature settling stability is 0.01 g/cm³, and the 1 d and 28 d compressive strengths of the set cement are 192. MPa and 27.1 MPa respectively, with no signs of strength decay observed. With the use of oil displacing weighted prepad fluid and the adoption of other well cementing techniques, the well Queshen-1 was successfully cemented.